Adding redundancy to your system can take two forms: adding spare capacity and
duplicating components.
It’s actually quite easy to add spare capacity—you can use any of the techniques
we’ve mentioned throughout this chapter. One way to increase availability is to create
a cluster or pool of servers and add a load-balancing solution. If one server fails,
the other servers take over its load. It is generally a good idea to underutilize your
components if you can, because it gives you much more “headroom” to handle performance
problems caused either by increased load or by component failures.
For many purposes, you will need to duplicate components and have a standby
ready to take over if the main component fails. A duplicated component can be a
simple as a spare network card, router, or hard drive—whatever you think is most
likely to fail.
Duplicating entire MySQL servers is a little harder, because a server is useless without
its data. That means you must ensure that your standby servers have access to
the primary server’s data. The following sections discuss some ways you can accomplish
this.
